[FFmpeg-user] Causes of color bars?

[Simon]

I think I have determined that as far as ffmpeg is concerned there is no
input. I added the flag -color_bars false, which I believe tells ffmpeg not
to display color bars in response to lost input. Sure enough, the color bars
went away. I interpret this as telling me that there was no signal, as
opposed to there being a signal that contained color bars.

So now, assuming my logic is sound, my question would be how can ffmpeg
detect the connected signal is present (it "knows" which channel is "live")
and yet not read the video signal?




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